Method of and means for heat treating glass articles



NIN

BY @MW M A TTORNEYS Patente July 30, 1935 UNlTso s'mTs PATEt oeiceMETHOD F AND MEANS FR,

TREATENG GLASS Robert G., Sherwood, lornng, N. *L assigne-r to (Corni-mgGloss Works,

sation oi? New Yon-k Earning, N, Y., o cofoo= Application May 25S, 1933,Serial No. 55%,@94

F Claims.,

5 creates compressionol sti'esses izo the euoce Tey- .1 tailed to giveaccurate conteoi ci the imei sties ers of the glass togetiiesl wittheeoofoemeot of the accompanying teosionel stesses to tile :lete'icr ofthe glass. @n the othei heed, meollo@ of glass articles depends upon theeiimioetioo of stresses oithe :tecluction tl'ieeof o negligible amount.

Prior methods of foi* the loom-cees stated have, as for es lmovm to me,involved the uniform heating of time ecticie toe temeeretuse above thestrain point. tempeiwtii'e in tempering is in cetelii ceses conteomoet?. above such point to accentuate effects ci tempering. annealingthe tempeetue is eiseol es high tout the heet is pioionged, one causesthe zeleese er the so-eeiiet cocinan-ent stresses which lood been ieftio the gore ous cooling. The eticle is there cooled et such e rete thatthe stiesses resulting toesecom will be small oia large es desire the"result-l ing average permeroemt stzess is is considered to loeemieelecl. compressional sti'ees is oree soostwotielly uniform thearticle is tempered ered stseogthened through the tooglteniog of itssoit-foce legoers, This uniform heating lees ocio? ort eeen followed leyooi-fom cooling ci the eiticle,

of Where e, noti-mitoyen stre is de sited, by non-uniform cooling; oftheThe prior method of effecting Y glass for the stated poi'poses heeezmecl teg, ilotion only of e, miccom comme of heet, socle es e. flameo? on electric resistoiice eiemeiet, end loes negiecteltlie conditions ointermeciete eiements, suelo as tile wolis of e mule oi chamber which isbooted from the outside oy the ommen? source end transmits heet to theieteior of the chamber.

Prior methods of cooling giace ari s how condition ceceuse they tieveeilec. to ovei'come the difcultydue to the teo-:ieocy o edge voiumeloi., flee-e5) production and distribution of pei-menen? stress in glassarticles by controi o oee eef, es i have found that the esL eci cootoistess con be "cest obtained by non-uniorm heating oi the glass followedby cooking under im'oim condtioos.

Toe above and other objects :mov ce etteineo" by oectlcmg my t iicliembodies among its :features heating e glass efticie by dient heat in o,controlled, mozuniomi menne? to establish predetermineci eretu'fe entsin e, direction parallel 'the surface theeof and lsubjecting the e touniform cooling conditions.

the novel con gement of ports to be more fully descbeo Merci-; claimed.in the appended claims, and iius in the eccompenying drawing, in whicWe. i is o vertical ee'tionel view of e heating glass sheets in accidonee inventioz;

Fig. 2 is e, front elevettioiz one of tice adieting elements of Fig. lslr-wing tl e fece thereof in eccorcionce with my invention;

Fig. E is o front elevetioi'i of e, modified. i-ietu ing element mede inaccordance with my invention;

Fig. e vetice for heating gloss bekiog dishes in accoiclence with myinvention;

5 is e view of "fie :fece of the upper :tedietioe element of Fig. 1L;

o is e, plan view of sie fece o1 redietiig eement of In prior methodsthe eticle is heated 'to e, pedeteimined uniform temperature and is thencooled. Frio? tempei'iug the iower mote trom the edge om?. thensubjecting it to uniform cooling conditions, 1:1 etefebiy e. eine berwhose tempeatute com. be A- einteimei substentielly unifoim tiloug'iioutemi ve ed f" siied, the tenflency of the to coo moi-e epidly con becompense-tec?. ti-1e motieven stieeses ettenclent thereon time ceeliminated.

-Foi exemple, in l have shown o device constructed in accorde-nce myinvention for nesting glass sheets in e tion-uniform manner.

The device comprises radiating elements i0 and I I which are formed ofcest iron or other suitable sectional view of e. device 4.

Acoeiiicient than the borders.

heat conducting material and which have projecting flanges l2 and I3around their edges. These elements are provided with suitable heatingmeans which in the present case comprise electric resistance elements Itand l5 disposed behind the faces thereof and which are adapted to heatthe faces of the radiating elements in a uniform manner. The radiatingelements may be hinged or slidably mounted to permit their beingseparated or brought together and when in the closed position as shownthe flanges l2 and i3 butt together to form a chamber I8. A sheet ofglass I9 is supported in the chamber I8 by any suitable means, as bytongs 2li. The distance between the glass surface and the facesof theradiating elements should preferably be relatively small.

In order to heat the glass sheet non-uniformly, that is, for example, toheat the edges to a higher degree than the center, the character of thefacesv of the elements Iii and il is made to vary from the centers tothe borders thereof with respect to radiation coefiicient, the centershaving a lower Regions 2i and 22 of the faces of the elements il) and Hwhich are adjacent the edges of the glass sheet are blackened orotherwise rendered heat radiating. Portions 23 and 26 of the surfaces ofthe elements which are adjacent the central portion of the glass sheetare polished or otherwise rendered less heat radiating. This is moreclearly shown in Fig. 2 which, although it represents the face of theelement l0, is also illustrative of the face of the element Il. In anarea 25 between the regions 2i and 23 the radiating property of thesurface varies progressively from the relatively high value of region 2ito the relatively low value of region 23. The surfaces which have thelower radiation coeicent may comprise a chromium plate or other suitablyresistant surface of a variable degree of polish. The surfaces of higherradiation coeicient may consist of a coating of lamp black or graphiteof a variable degree of density.

It will be noted that in my device the elements iii and il constitute anintermediate source of heat and that heating of the glass isaccomplished by means of the heat which is'radiated therefrom. Inaddition, control of heat may be obtained by regulation of thetemperature of the'resistance elements ld and i5 which in the presentexample constitute the primary source of heat. Glass absorbs asubstantial amount of radiant energy and, being partially transparentthereto, such energy is absorbed practically simultaneously anduniformly throughout the body of the glass. Radiation heating thereforeprcduces in glass a substantially uniform temperature between thesurfface and the interior, thus avoiding objectionable temperaturegradients which are normal to the surface. For this reason, also,heating throughout the mass can be accomplished more rapidly byradiation heating than by conduction heating and the 'liability ofbreakage due to thermal shock will consequently be less. l 4

To `treat a glass sheet I heat the sheet by means f the above describedapparatus in a non-uniform manner to a temperatureabove the strain pointso as to establish predetermined temperature gradients in the glass andparallel with its surface in such a manner that upon subsequent free ornatural cooling of the sheet either in air or in a uniformly heatedchamber a uniform final stress condition is obtained whiclP may be largeor small as desired, depending upon the aooavas rapidity of cooling. Forexample, the resistance elements it and i5 (Fig. 1) are energized so asto heat the faces of the elements lll and Il uniformly to a temperatureabove the strain point of the glass which is to be treated and a sheetof glass is supported in the chamber i8. Alternatively, the glass sheetmay be placed in position before the elements lo and Il are heated andthe glass-may be initially hot or cold. Since the areas 2i and 22 of thefaces of the elements have a higher coefficient of radiation than theareas 23 and 2d, the areas 2i and 22 will radiate more heat and theedges of the glass sheet will become heated to a higher temperature thanthe central portion. Heating is continued until the central portion ofthe glass sheet has reached a temperature sumciently above the strainpoint of the glass to permit any prior permanent strain to be relievedwithin a reasonable time. After the glass sheet has thus been heatedto anonuniform temperature labo-ve the strain point and the all previouslyexisting strain substantially removed it is taken from the heatingdevice and allowed to cool in the usual manner either in the air or in auniformly heated chamber, depending upon the amount of residual straindesired. If iheproper temperature gradient between the edges and centralportion of the glasssheet has been established the residual strain willbe uni'- form throughout the glass and may be large or small, dependingupon the rapidity of cooling. Since the temperature gradient which willproduce a uniform stress condition on cooling and since the cooling ratenecessary to establish the desired amount of stress will vary withconditions such as thickness of the glass sheet and the expansioncoeflicient and other physical properties depending upon the compositionof the glass, it will be obvious that the variation in radiationcoemcient of the radiating faces which is necessary for the heating ofall sheets of glass cannot be stated. However, the proper variation forany given sheet of glass can readily be determined by trial.

IfV it is desired to produce in a glass. sheet a predeterminednon-uniform strain pattern by forming a corresponding pattern ofcompressional stresses in the surface of the article the variableradiating portions of the elements can easily be arranged in the propersequence and with the u proper difference in radiation comcients toobtain this result. It may also be desirable to have the strained areasof the glass more or less sharply outlined in order to intensify thoseproperties which are associated with stress. Such a distribution ofstress may be obtained by varying more or less abruptly the coemcient ofradiation of the various regions of the surfaces of the radiatingelements from relatively high radiation to relatively low radiation. InFig. 3 I

have shown a radiating element 26 the face of-` which bears on arbitrarydesign composed of highly radiating areas 2l and slightly radiatingareas Q6. It is to be understood that the design shown is purely`arbitrary for the purpose of illustration and that this design may takeany desired form. f

The method above described for the heating of glass sheets is likewiseapplicableto other glass articles such as baking dishes and the like andsuch articles can thereby be annealed sov as to be free from the usualrim strain or they can be vmade to acquire a. uniform or non-uniform Yvcompressional stress over the entire surface as desired in order toincreasethe mechanical and thermal strength or to give them definitebreaking characteristics as the case may be. In Fig. 4 an upperradiating element 29 rests upon a lower radiating element 30 in such amanner that a truncated conical extension 3| of the element 29 projectsinto a corresponding cavity 32 of the element 30 to form a dish-shapedchamber 33. Within the chamber 33 a glass baking dish 34 rests uponpointed supports 35 of non-conducting material such as transite, lireclay, or the like, so

that the dish 34 is not in contact with the walls of the chamber 33. Theelements 29 and 30 are provided with suitable heating means which in thepresent case comprise electric resistance elements 35 and 3l disposedbehind the faces thereof and adapted` to heat the faces of the elements29 and ina uniform manner. The elements 29 and may he hinged or mountedin any suitable manner to facilitate their being separated or broughtinto closed relation. As in the case of the elements i ti and l I shownin Figs.2 and 3, the faces or" the elements 29 and 30 have a varyingcoerlicient of radiation. In order to treat the dish 35i so that it willhave a uniform stress or freedom therefrom it will be obvious in view ofthe foregoing that those portions of the faces of the radiating elements2Q and 3G which are adjacent the rim of the dish 34 must have a highercoefcient of radiation than the portions which are remote from the rimand that the remote portions must have a relatively lower coefficient ofradiation. This is illustrated in Figs. 5 and 6 where the shaded area inthe peripheral regions of the radiating faces indicate regions ofrelatively high radiation coefficient. The regions of relatively highand low radiation ca also be arranged in any suitable manner to produceany desired strain pattern as is illustrated in Fig. 3. As pointed outabove, the difference in coeicient of radiation of the various regionsof the radiating faces which is necessary for the proper heating of allglass articles can not be stated since this will vary with conditionsbut for any given glass it may readily be determined by trial.

While in the foregoing there has been shown and described the preferredembodiment of my invention. it is to be understood that minor changes inthe details of construction, combination and arrangement of parts may beresorted to without departing from the spirit and scope of the inventionas claimed.

l What I claim is:

1. In an apparatus for heating glass articles diate of the glass and theheating means, the` face of which adjacent to the glass is blackened inselected areas and polished in other areas, the degree of blackening ofthe blackened areas decreasing towards adjacent polished areas.

3. 'I'he method of heat treating a glass article which includes heatingthe article non-uniformly to a temperature between the strain point andsoftening point of the glass to establish suitable temperature gradientstherein parallel to the surface of the article and subjecting thearticle to uniform cooling conditions.

4. The method of heat treating a glass article which includes heatingthe edges of the article to a temperature below the softening point butabove the temperature of the central portion of thc article, saidcentral portion being heated to a temperature above the strain point ofthe glass and subjecting the article to uniform cooling conditions.

5. The method of heat treating a glass article which includes supportingthe article between heat radiating elements, the'faces of which have avarying coefficient of radiation, supplying heat to t' .e radiatingelements to heat the article by means of the radiated heat to establishsuitable temperature gradients in the article, the minimum temperaturebeing above the strain point of the glass, removing the article frombetween the radiating elements and subjecting the article to uniformcooling conditions.

6. The method of heat treating a glass article which includes supportingthe article between heated radiating elements, radiating heat from theelements into the central portion of the article to raise thetemperature of the central portion above the strain point of the glass,radiating suiiicient heat from the elements into the edges of thearticle to raise the edges to a temperature higher than the centralportion, removing the article from between the elements and subjectingit to uniform cooling conditions.

ROBERT G. SHERWOOD.

